package jp.co.hcs.attendancemanagement.filter;

import java.io.IOException;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;

/**
 * <p>
 * Example filter that sets the character encoding to be used in parsing the incoming request,
 * either unconditionally or only if the client did not specify a character encoding. Configuration
 * of this filter is based on the following initialization parameters:
 * </p>
 * <ul>
 * <li><strong>encoding</strong> - The character encoding to be configured for this request, either
 * conditionally or unconditionally based on the <code>ignore</code> initialization parameter. This
 * parameter is required, so there is no default.</li>
 * <li><strong>ignore</strong> - If set to "true", any character encoding specified by the client is
 * ignored, and the value returned by the <code>selectEncoding( )</code> method is set. If set to
 * "false, <code>selectEncoding( )</code> is called <strong>only</strong> if the client has not
 * already specified an encoding. By default, this parameter is set to "true".</li>
 * </ul>
 * 
 * <p>
 * Although this filter can be used unchanged, it is also easy to subclass it and make the
 * <code>selectEncoding( )</code> method more intelligent about what encoding to choose, based on
 * characteristics of the incoming request (such as the values of the <code>Accept-Language
 * </code> and <code>User-Agent</code> headers, or a value stashed in the current user's session.
 * </p>
 * 
 * @author Craig McClanahan
 * @version $Revision: 1.5 $ $Date: 2005/03/21 18:08:09 $
 */
public class SetCharacterEncodingFilter implements Filter {

  // ------------------------------------------------- Instance Variables

  /**
   * The default character encoding to set for requests that pass through this filter.
   */
  protected String encoding = null;

  /**
   * The filter configuration object we are associated with. If this value is null, this filter
   * instance is not currently configured.
   */
  protected FilterConfig filterConfig = null;

  /**
   * Should a character encoding specified by the client be ignored?
   */
  protected boolean ignore = true;

  // ----------------------------------------------------- Public Methods

  /**
   * Take this filter out of service.
   */
  public void destroy() {
    this.encoding = null;
    this.filterConfig = null;
  }

  /**
   * Select and set (if specified) the character encoding to be used to interpret request parameters
   * for this request.
   * 
   * @param request The servlet request we are processing
   * @param result The servlet response we are creating
   * @param chain The filter chain we are processing
   * 
   * @exception IOException if an input/output error occurs
   * @exception ServletException if a servlet error occurs
   */
  public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
      throws IOException, ServletException {

    // Conditionally select and set the character encoding to be used
    if (ignore || (request.getCharacterEncoding() == null)) {
      String encoding = selectEncoding(request);
      if (encoding != null) {
        request.setCharacterEncoding(encoding);
        response.setCharacterEncoding(encoding);
      }
    }

    // Pass control on to the next filter
    chain.doFilter(request, response);
  }

  /**
   * Place this filter into service.
   * 
   * @param filterConfig The filter configuration object
   */
  public void init(FilterConfig filterConfig) throws ServletException {
    this.filterConfig = filterConfig;
    this.encoding = filterConfig.getInitParameter("encoding");
    String value = filterConfig.getInitParameter("ignore");
    if (value == null)
      this.ignore = true;
    else if (value.equalsIgnoreCase("true"))
      this.ignore = true;
    else if (value.equalsIgnoreCase("yes"))
      this.ignore = true;
    else
      this.ignore = false;
  }

  // -------------------------------------------------- Protected Methods

  /**
   * Select an appropriate character encoding to be used, based on the characteristics of the
   * current request and/or filter initialization parameters. If no character encoding should be
   * set, return <code>null</code>.
   * <p>
   * The default implementation unconditionally returns the value configured by the
   * <strong>encoding</strong> initialization parameter for this filter.
   * 
   * @param request The servlet request we are processing
   */
  protected String selectEncoding(ServletRequest request) {
    return (this.encoding);
  }
}
